@Anonymous wrote:I understand its optimal to keep utilization at 10 percent. Is that on 10 percent of that one card's limit or is it of your total credit available across all cards?
Its actually below 10% and its of one cards individual CL the rest of your revolving lines at 0
@Anonymous-own-fico wrote:There is no such utilization percentage for one, some or all cards. Less is generally better, but that's about it.
Well holdup a second 
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I absolutely agree that the common advice given here isn't entirely accurate for all people but to suggest that the computer algorithm which determines one FICO score doesn't use pretty standard math to determine one's score is sort of absurd.
I'll admit there may be different utilization breakpoints for different individuals, but at some point there has to be a line drawn and that line cannot be random. The algorithm may not ever be exactly known, but it can be tested... just most people don't really care enough to do so, or don't have the file / discipline to get good data points. Or money 
End of the day the "all cards except one reporting $0, and that one reporting <10% of it's limit" mantra is pretty good for pretty much everyone and for the vast majority of the credit universe leaving a couple FICO points on the ground isn't a big deal. As an example where it's not 100% I know for a near absolute fact with my report that 1 vs 2 revolving tradelines reporting a balance doesn't matter at all, but I also have 9 credit cards: I don't take a hit until I have 3/9 reporting. Other people who are testing that have less credit cards, have found it does indeed make a difference for them. I also don't take a hit for having 1/9 reporting, my score is identical when I optimize my reports with either 1 or 2/9 cards reporting a balance so it's not like the 1/9 is bad advice for me.
It could be a straight percentage, three easy numbers: 25, 30, 33% could be the breakpoints, and that is absolutely testable in my opinion as an example, just need more clean data.
Fact is the computer isn't playing pin the tail on the donkey to determine our score: it is an algorithm, it is implemented by a computer, the broad strokes of it can be determined.
ETA: another fact, simple is good: the mantra is easily understood by the people who find this forum and if they generally go off and chase that their FICO scores will improve. The algorithm is absolutely more complicated than that, but if we do determine it's say <33% of cards reporting balance, suddenly people have to do math, and that is just going to confuse the issue more when below whatever break point doesn't make any difference. If I weren't geekily interested in the algorithm, simple fact is that it would be absolutely irrelevant in my world as I know I can hit my max scores (approximately, small utilization might make a difference) with a small balance on one of my credit cards... and that's good enough for any practical purposes I have, including mortgage qualification which I rate as the most important thing in the credit universe.
@Thomas_Thumb wrote:From a variety of published articles there are some recurring rules of thumb as follows:
1) Keep each individual card's utilization under 20% and overall combined utilization under 10% for max FICO score.
2) Exceeding 30% utilization on a card usually results in a FICO score drop even if overall utilization is under 10%.
3) Exceeding 75% to 80% utilization on a card is a red flag as it is considered maxed out. This can result in a substantial drop in FICO scores even if overall utilization is under 10%. The amount of drop depends on your score before the high utilization is posted.
4) Consistent overall utilization 20% and above is viewed negatively by scoring models and will keep you from reaching a top score.
Using only one card and having the others report a zero balance is not not necessary for high scores but it won't hurt either. However, it is best to not carry a balance on more than half of your credit cards at any one time. Based on experience it appears that Fico 8 considers payment amount vs balance and can determine when balances are paid in full without the need to show zero balances. I don't think the Fico 4 model has that capability.
I show monthly balances on a number of cards but maintain utilization under 15% even on my primary card (under 6% overall) and always pay every card in full each month.
Fico 8: EQ 850 TU 850 EX 850 (MyFico 3/2015)
Fico 4: EQ 796 TU 823 EX 830 (MyFico 3/2015)
Fico 98: EX 839 (MyFico 3/2015)
Published articles are pretty much junk, especially as they don't state sources.
Much better information can be found here typically; while I agree there's some more concrete testing needed, I'd take anything I've read online with a grain of salt as the exact mechanics of the algorithm will never be disclosed. The fact is with the number of people testing here and elsewhere over time, it's better than one shot in a vacuum which is at best what they've got in many cases.
I would strongly suggest you do your own testing before making blanket statements on the algorithm, especially ones that we've found anecdotally through testing to be inaccurate. While I would agree we absolutely don't know everything, most of the articles which are posted regarding credit scoring provide much hilarity both here and other similar sites.
@Thomas_Thumb wrote:John Ulzheimer is a rather good resource as he worked for FICO for many years and has since published a book on the subject. You may want to check out his book "Smart Consumer's Guide to Good Credit" and search for articles he has authored. There are a number of other informative books on the subject and useful articles from Credit Karma, TransUnion and elsewhere.
My Fico 8 scores have reported at 850 every month since 2/2014. I do know how many credit cards I used, what balances I have carried what my percent utilization has been during this time frame. I typically have reported balances on 4 of 9 credit cards each month but always pay in full. A few months I only carried balances on two cards. Overall utilization has been maintained below 6% at all times.
I have never subscribed to using only one card and having all others report at zero balance. Although that approach won't hurt your scores it over complicates managing ones credit and can divert focus from basic fundamentals such as: credit utilization management, paying cards in full each month and managing ratio of monthly debt payment obligations to income.
My Fico 4 scores do fluctuate some and they took a hit when I allowed one card to post a high utilization of 80 % one month - even though I paid it in full. Interestingly, my Fico 8 score never dropped from 850 - so I feel reasonably comfortable in my belief that Fico 8 factors in payment relative to balance (e.g. current month payment vs prior month balance to evaluate payment in full) but that the Fico 4 model likely does not.
My comments might conflict with your beliefs but the comments are based on personal experience along with information gleened from a variety of sources including: statements in personal EQ, EX and TU reports, MyFico 3B report, published books and cross referenced internet articles.
There is a wealth of information/data posted on MyFico and everyone has their own experiences with differing results and outcomes.
The aforementioned expert is bound not to reveal exact information regarding the algorithm. Confidentiality and Non-disclosure agreements. Credit Karma is laughable in it's advice FWIW and many of their articles are not much better.
Your own personal experiences are just that, and it has been demonstrated that an 850 (only recently possible with the release of the FICO 8 algorithm btw) is possible with minor "blemishes" on one's report such as suboptimal balance reporting, and beyond that one's score really provides no relevance to their knowledge of the mechanics of the algorithm: you do not earn respect here or elsewhere with one's credit score. As a further example, balances have been demonstrated to be instant in time for the overwhelming amount of evidence ever provided: you need to look no further than the massive upswings in score people receive when using when consolidating their revolving debt with an installment loan.
I would be the first to admit the information here isn't perfect, and I know for a fact I have no difference in my credit scores (except TU Bankcard 04) if I have 1 vs 2 revolving trades reporting a balance. Additionally, I have incredibly few beliefs and absolutely none regarding the FICO algoritm; however, I do subscribe to evidence based on tests, which you have not provided for your assertions. When you have data points to support some of your opinions, all of us will be happy to listen to your evidence.